Radio frequency (RF) communication systems that make use of time division multiplexing (TDM) are known. In such systems a communication frequency (or pairs of frequencies) is divided by time into frames and time slots, and a plurality of communication units are assigned time slots to support their communication needs. The communication units communicate their messages at their respective assigned time slots through a number of repeaters in conjunction with one central communication controller. To facilitate the channel assignment mechanism, such systems generally provide one or more dedicated control time slots that support the channel assignment and other control functions.
An important feature of a TDM radio communication system is the capability of providing full duplex communication between two communication units. In a conventional implementation of a full duplex TDM system, the repeater communicates communication messages with a first and a second communication unit on inbound channel and outbound RF channels. The first communication unit transmits, on the inbound channel, a communication message during a first assigned inbound time slot which is repeated by the repeater on the outbound channel and received by the second communication unit during a first assigned outbound time slot. The second communication unit transmits a communication message during a second outbound time slot and, likewise, this communication message is simultaneously repeated by the repeater and received by the first communication unit during a second inbound time slot. Thus, for each call, two outbound time slots and two inbound time slots of the repeater are utilized. A major problem with this arrangement is that the amount of inbound and outbound time slots, i.e. the spectrum, required for providing a full duplex communication system substantially limits the total system capacity for a given spectrum allocation, thereby restricting additional enhancing features to be incorporated in the system.
Therefore, a need exists to efficiently utilize the available spectrum and provide additional features or capacity for carrying out a full duplex communication between two communication units.